On Mon, 25 Oct 2021, Ron Garret wrote:
Note that message-ids are not guaranteed to be unique. During my test
I found groups of as many as 20 different messages with the same
message ID. (Turns out this makes quite a reliable spam signal!)
It's by far not a rare situation: duplicate message-ids happen whenever
the sender names more than one local recipient during SMTP. It's a wholly
unreliable way to indicates spaminess. However, if a high proportion
of those recipients do not exist, ...
I think you may have misunderstood. What you say isn?t wrong, but in
the case of multiple local SMTP recipients, all of the duplicate
messages will have the same content. What I have found is the same
message ID in messages with (very) *different* content (and often sent
to the same user). All of that has been spam (and it is hard to
imagine any situation in which it would not be).
Ah, that is a different situation. It could happen if the same message
tooks different paths to your user e.g. via mailing list processor,
but that is less common and would probably break DKIM.
Joseph Tam <jtam.h...@gmail.com>
